Memory will clock down to run at optimal speeds depending on processor model installed. See latest ProLiant QuickSpecs for processor models and supported memory speeds.
If only one processor is installed, only 12 DIMM slots are available. When populating with two processors 24 DIMM slots are available.
White DIMM slots designate the first slot of a channel. For 1 DPC (DIMM per channel) populate white slots only.